Automated vehicles and guidance systems associated therewith have been commercially developed whereby the vehicles effectively "track" a predetermined guide path comprising guide lines on a floor surface. Exemplary vehicles and guidance systems are disclosed in commonly assigned U.S. Pat. Nos. 3,935,922; 3,970,840; and 4,003,445. The vehicles disclosed in these patents can be adapted for specific uses such as floor maintenance, mail delivery, and similar functions routinely performed within industrial and commercial organizations.
When these vehicles are performing functions such as mail delivery and material handling, the organization to be serviced can require two or more vehicles to be operating simultaneously. Further, the structural "layout" of the organization can require the guide path to comprise intersecting guide lines and predesignated sections such as "unloading" zones and the like.
As the nature of guided vehicle functions become more sophisticated, and as the user organization places increasing reliance on the vehicles by simultaneously employing an extensive number thereof, an increase in the probability of "hazardous" situations becomes apparent. For example, the simultaneous use of two or more vehicles on a guide path having intersecting guidelines implies a finite probability of collision. To minimize this probability, a collision avoidance system can be utilized. However, such a system must be capable of not only preventing collisions, but must do so in an optimal and efficient manner which does not cause traffic "bottlenecks" or similar situations necessitating manual intervention.
Several prior art systems include apparatus directed to collision avoidance between driverless vehicles which automatically follow various types of guide paths. For example, the U.S. patent to Schonbrodt U.S. Pat. No. 3,594,571, issued July 20, 1971, discloses a collision avoidance system for two driverless vehicles traveling in the same direction along a guide rail. The guide rail comprises overlapping conductor loops disposed on opposite sides thereof. Transmitters mounted on the vehicles provide signals which can be received by other vehicles. Various circuit apparatus causes the following vehicle to stop if it is within the same conductive loop area as the leading vehicle. However, the Schonbrodt system does not appear adaptable to systems employing embodiments thereof for more than two vehicles or having vehicles which track along separate but intersecting guide lines.
The U.S. patent to Hartley U.S. Pat. No. 3,610,363 issued Oct. 5, 1971, discloses an automatic vehicle guidance system having "decision" points disposed along a track layout and circuitry at each decision point for deriving the unique identity of a vehicle arriving thereat. All of the vehicles are controlled from computer apparatus remote from the vehicles and track layout. The centralized computer complex is capable of applying "run" signals to the individual vehicles and to inhibit such signals if received data indicates that other vehicles are on the track to which the identified vehicle is to be transported. This system has the limitations of requiring a fairly complex centralized computer system for purposes of control and further requiring substantial information to be transmitted between the guide track system and the central computer.